Conservation and Architecture of TlpD.
(A) H. pylori inner-membrane–bound (yellow arc) chemoreceptors TlpA-C and cytosolic TlpD control the autophosphorylation of CheA to CheA-Pi, which then transfers the phosphate to CheY, and CheY-Pi can interact directly with the flagella rotor (pink) to cause a temporary reversal in flagellar rotation. Flagella reversals cause direction changes in swimming trajectory (dotted lines). Black arrows show signal transduction for a chemorepellent response. (B) Two sets of chemoreceptor trimers of homodimers (light and dark blue, denoted as Tlp) associate with the scaffold protein CheW (gray) and a CheA dimer (light and dark orange) to form the core signaling unit and modulate CheA autophosphorylation (illustrative model based on PDB code: 3ja6). (C) A relatedness tree of TlpD protein sequences from Helicobacter (blue), Deferribacteraceae (purple), and other species. H. pylori TlpD (arrow) is nearly identical to species found in dolphins and cheetas (red dot). (D) A theoretical model of a HpTlpD monomer constructed by i-Tasser with an N-terminal region of unknown structure (light green), the canonical coiled-coil domain of chemoreceptors that interfaces with CheW and CheA (light blue), and a CZB domain (dark blue). Sequence conservation among 459 TlpD homologues is mapped onto the model with 100% conservation highlighted in red and >95% conservation in orange. Cys residues present in the SS1 strain of HpTlpD are noted with green circles. See Zähringer and colleagues  for a theoretical model of the TlpD dimer. (E) Conservation of each Cys residue in TlpD is shown with 2 Weblogo plots ; the left shows conservation among all sequences of HpTlpD (394 sequences, >92% sequence coverage, >98% sequence identity), and the right plot is conservation among nonpylori TlpD sequences (68 sequences, >91% coverage, >40% sequence identity). Only C340 is universally conserved among all TlpD homologues (noted with * in panels E and D). CheA, chemotaxis protein A; CheA-Pi, phosphorylated CheA; CheW, chemotaxis protein W; CheY, chemotaxis protein Y; CheY-Pi, phosphorylated CheY; CZB, chemoreceptor zinc-binding; HpTlpD, Helicobacter pylori TlpD; PDB, Protein Data Bank; TlpA-C, transducer-like proteins A-C; TlpD, transducer-like protein D.